10.14 爱奇艺AC3 求各位大佬指正

//五个式一个循环
//每次都拿5的倍数，位数是1 4 6，拿不了的话就是尾数6，等于拿了1，自己试试就知道了
#include<bits/stdc++.h>
using namespace std;
int main(){
    int t, n;
    while (cin >> t){
        while (t--){
            cin >> n;
            switch (n % 5){
            case 1:cout << "niu" << endl; break;
            case 2:cout << "yang" << endl; break;
            case 3:cout << "niu" << endl; break;
            case 4:cout << "niu" << endl; break;
            default:cout << "yang" << endl; break;
            }
        }
    }
}
//这个当前点是子串的最大或次大，遍历一下
#include<bits/stdc++.h>
using namespace std;
void swap(int &a, int &b){
    int t = a;
    a = b;
    b = t;
}
int main(){
    int n;
    while (cin >> n){
        vector<int> v(n);
        for (int i = 0; i<n; i++)cin >> v[i];
        int res = INT_MIN;
        for (int i = 0; i<n; i++){
            int s = i - 1, e = i + 1, maxval = v[i], secval = v[i];
            while (s >= 0 && v[i] >= secval){
                if (v[s]>secval)secval = v[s];
                if (secval>maxval)swap(secval, maxval);
                if (maxval != secval)res = max(res, maxval^secval);
                s--;
            }
            maxval = v[i], secval = v[i];
            while (e<n&&v[i] >= secval){
                if (v[e]>secval)secval = v[e];
                if (secval > maxval)swap(secval, maxval);
                if (maxval != secval)res = max(res, maxval^secval);
                e++;
            }
        }
        cout << res << endl;
    }
}
//期望题，动态规划递推就好了
#include<bits/stdc++.h>
using namespace std;
double dp[55];
double Cn2(int n){
    return (double)n*(n - 1) / 2.0;
}
int main(){
    int n, m;
    double res;
    cin >> n >> m;
    dp[0] = 0;
    dp[1] = Cn2(n + m) / (n + m - 1);
    for (int i = 2; i <= m; i++){
        dp[i] = (i*(m + n - i)*dp[i - 1] + i*(m + n - i) + Cn2(i) + Cn2(m + n - i) + Cn2(i)*dp[i - 2]) / (Cn2(n + m) - Cn2(n + m - i));
    }
    printf("%.1f\n", dp[m]);
}